But whether you use Cost Focus or Differentiation Focus, the key to making a success of a generic Focus strategy is to ensure that you are adding something extra as a result of serving only that market niche. It's simply not enough to focus on only one market segment because your organization is too small to serve a broader market (if you do, you risk competing against better-resourced broad market companies' offerings.)
The "something extra" that you add can contribute to reducing costs (perhaps through your knowledge of specialist suppliers) or to increasing differentiation (though your deep understanding of customers' needs).